Ever wondered what those Matrix-style green holographic codes that flicker across computer screen in films actually mean? You know, those seemingly complex algorithms in The Fifth Estate and unbreakable cryptograms in Doctor Who? Well, programmer John Graham-Cumming has the answer.

"I was watching the film Elysium and some coding came up as the space station is rebooted, and I thought: 'This is really familiar', so I tracked it down," explains Graham-Cumming, who started coding at the age of 13 on his BBC Microcomputer and is now a well-known blogger and programmer. "It turns out that the code is actually taken directly from the Intel software developer's manual, which I found amusing. So I tweeted that and got hundreds of responses." Last Friday, he launched a Tumblr to compile more examples; by Monday morning it already had 11,000 followers and Graham-Cumming was inundated with suggestions for movie codes to crack.

Code from Elysium. Photograph: John Graham-Cumming/Tumblr

The process of identifying the sources of movie codes is actually quite simple. Graham-Cumming takes a screengrab and immediately gets a sense of whether the code is possibly legitimate or utter nonsense. If an unusual character or variable stands out, he picks it out and Googles it. In most cases, whether the codes is purporting to guide a missile or rifle through confidential databases, it's likely to be a pretty mundane cut and paste job.

There are some real howlers. Graham-Cumming was tickled while watching Antitrust, a thriller about a wannabe Bill Gates: "I cracked up watching these computer nerds looking at code, nodding and saying: 'Whoa, this is great man,' when it was really the most basic Java script that is completely meaningless." In The Terminator, we see the world through T-800's head-up display, yet the scrolling text accompanying the crosshair in his vision is the harmless assembly code for an Apple-II. But the sources for fake coding just get better: in one episode of Doctor Who, Matt Smith looks intently at some hovering code, yet on closer inspection, it's the reference for a simple image file – a picture of a lightwave – lifted from Wikipedia.

Code in The Terminator Photograph: John Graham-Cumming/Tumblr

Computer programmers must laugh when they see characters in films adjusting their thick-rimmed glasses, furiously typing, then gazing at a code that probably only says: "Hello world." Graham-Cumming finds it surprising, though, that these details, which might be central to a plotline, are rarely given more thought and attention by directors, particularly as plausible codes are so easy to find through open–source websites such as GitHub and SourceForge.

However, there are some impressive examples of programming detail. Jurassic Park was clearly ahead of its time: actors worked on realistic, high-performing Silicon Graphics computer systems and in one classic classic scene, teenager Lex Murphy logs on to the computer and exclaims: "It's a Unix system, I know this," which relates to a real operating system.

Code in The Girl with the Dragon Tattoo. Photograph: John Graham-Cumming/Tumblr

More recently, The Social Network provided a visually compelling, technically authentic narrative about the process of programming. When Mark Zuckerberg, played by Jesse Eisenberg, types the commands for "facemash" using PerlScript, it is woven in with his explanation of the procedure in plain text and HTML on his blog. In David Fincher's The Girl with the Dragon Tattoo, heroine Lisbeth Salander is depicted as searching for files using the same process that real developers use. With the rise of high-definition screens and screen-capture tools, and with gadgets such as Google Glass increasingly likely to be used on screen, there will only be more opportunities for smart-ass code-reading. Directors take note.